The invention relates to door structure for transportable cargo containers such as those which may be used on ships, rail lines, and trucks. More particularly, the invention relates to an improved cargo container door which is light in weight and economically manufactured, but which has high strength and durability in service.
Cargo container doors have often included a relatively heavy metal outer panel, or a lighter panel with some form of stiffening attached to the inside or outside surface. The stiffeners often took the form of elongated metal sections, U-shaped in cross section, which were welded along their edges to a surface of the panel. While generally supplying the required stiffness, these stiffener members required a high number of welds. They also demanded a large quantity of material and occasioned the occurrence of many interior, inaccessible cavities and niches where moisture would be retained and rust would collect. At the door edges, this type of door often had some form of tubular frame, which also added to the problem.
Prior container door constructions, including the types described above, were considerably heavier and more costly than the construction of the present invention described below, while being no stronger than the present construction and actually being less durable, due to the tendency for rust to occur.